1. Field of the Invention
This invention relates to improvements made to piston pumps of which the seal between the piston and the cylinder bore consists of an rolling membrane.
2. Histroy of the Related Art
This membrane type of seals for piston pumps is known to allow for a longer piston stroke and perfect sealing. Unfortunately, it is practically impossible to use such an rolling membrane on sucking and forcing pumps due to the depression resulting from the sucking phase. The piston motion causes partial vacuum inside the cylinder, so that the membrane does not keep flat against the piston periphery, starts folding inside the cylinder and wears out very quickly.